This section provides background information related to the present disclosure which is not necessarily prior art.
Permanent magnet motors typically include a stator and a rotor that rotates within or around the stator. The speed and angular position of the rotor are commonly used to generate control signals for the motor. Traditionally, the speed and angular position of the rotor are determined via one or more rotor position sensors. More recently, techniques have been developed and used for determining the speed and angular position of the rotor sensorlessly (i.e., without direct measurement of the rotor speed or position). For example, flux of the motor may be estimated and used to estimate the rotor speed and/or position. The estimated flux is not used, however, when starting these motors. Instead, the motors are controlled without relying on estimated flux until a preset time period has elapsed, or until the motor reaches a defined speed, torque output, etc. At that point, the flux estimates are assumed to be sufficiently accurate, and the motor control begins using the estimated flux to control the motor.
After some period of time, and possibly due to some external factor, the flux estimate in the prior art controller could become unreliable. In that event, the rotor position and speed estimate become unreliable resulting in the drive tripping or problematic oscillation.